Thanks, so it's not possible to make a sequence over 2 indices in seq?

My take was:

@Mariusz Iwaniuk 

Thanks. I thought everyone here, except me was a H.Potter ;)

@Mariusz Iwaniuk 

I have 2017 so neither worked. But 

plot3d(add(op(1,U(x, t)), n=1..20, 2), x = 0 .. 6, t = 0 .. 4);

worked nice :)

@Rouben Rostamian  

@rlopez 

examples of how to deal with "unprojected" vectors?

@rlopez 

I even managed to get the acceleration right: 

Now I can go on with my study of vector calculus with a bit more confidence :)

@Kitonum 

I just wish though that it would be possible to get the answer explicitly in the new coordinate system. Couldn't find anything in the Physics package. A bit surprising.

@Kitonum 

Since the unit vectors rho hat and phi hat aren't constant like i hat and j hat they depend on t. So I would like to see e.g the velocity expressed in these unit vectors.

If r(t)=rho(t)*rho hat then

v(t)=rho dot*rho hat+ rho*phi dot*phi hat

How do I get that expression in maple?

@Kitonum 

Many thanks for the solution!

Thanks all for the help

@Rouben Rostamian  

I'm running 2015. Maybe that's why I have to add that

S

@Rouben Rostamian  

I suppose you wrote

SetCoordinates(cylindrical[r, phi, z])

otherwise I can't make it work

@Kitonum 

I have Maple 2017 but doesn't get any solution at all. How is that possible?

S

@tomleslie 

Thanks!

@Kitonum 

Seems it's not possible to use ^ in 2d math. Never thought of that.

restart;
z := -(4*b^2*d*p^2-3*c*g*p^2)/(4*(-u+L));
u := 2; L := 1; c := .6;
constr := [1-2*d/(p*(sqrt(g)+1)) <= b, b <= 1, 0 <= d, d <= L, c <= p, p <= u, 1 <= g, g <= 4];
Optimization:-Maximize(z, constr);
    [2.20000000000000018, [b = 1., d = 1., g = 1., p = 2.]]